Process for the preparation of menthol
Menthol was prepared under solvent-free conditions by using an ammonia-treated nickel-silica supported catalyst, which solved the problems of low selectivity and numerous byproducts in the prior art and achieved a highly efficient and simplified preparation process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HANWHA SOLUTIONS CORP
- Filing Date
- 2024-11-22
- Publication Date
- 2026-06-05
AI Technical Summary
In the existing technology, the hydrogenation reaction of thymol is difficult to simultaneously improve the selectivity of menthol, the reaction rate and the inhibition of by-product formation, resulting in long processing time, low conversion rate and excessive by-products.
Menthol was prepared by using an ammonia-treated metal-supported catalyst, such as a nickel-silica-supported catalyst, in combination with hydrogen under solvent-free conditions via the reduction reaction of thymol.
This method enables the efficient preparation of menthol at low temperatures and with low catalyst dosage, improving the selectivity of menthol, inhibiting the formation of hydrocarbon byproducts, simplifying the process, and increasing productivity.
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Abstract
Description
Technical Field
[0001] This disclosure relates to a method for preparing menthol from thymol. Background Technology
[0002] Menthol (2-isopropyl-5-methylcyclohexanol) is a useful material in various industries such as pharmaceuticals, cosmetics, and food. Menthol is a compound with three chiral centers, including four isomers: D / L-menthol, D / L-isomenthol, D / L-neomenthol, and D / L-neoisomenthol. Among these, D / L-menthol has the widest industrial applications.
[0003] In current industry, the hydrogenation of readily commercialized thymol (2-isopropyl-5-methylphenol) is primarily used to prepare menthol. However, improving the selectivity of menthol remains a challenge due to the complex mixture produced by the hydrogenation of thymol, which includes four isomers and menthane as a hydrocarbon byproduct. Various studies have been conducted to improve the selectivity of menthol, but methods involving multiple steps or reducing the reaction rate suffer from limitations such as excessive processing time and low conversion rates. Furthermore, even methods that enhance the hydrogenation reactivity often produce excessive byproducts, or result in a decrease or maintenance of the selectivity of menthol as the target product.
[0004] Therefore, there is a need for new technologies that can simultaneously satisfy the requirements of menthol selectivity, reaction rate, and byproduct inhibition. Summary of the Invention
[0005] Technical issues One aspect of this disclosure relates to a method for preparing menthol that simultaneously satisfies excellent reaction rate and excellent menthol selectivity.
[0006] Solution to the problem One aspect of this disclosure provides a method for preparing menthol, comprising preparing menthol by reduction of thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.
[0007] Metal-supported catalysts may include nickel-supported catalysts, which include one or more active metals selected from nickel and nickel oxide.
[0008] Metal-supported catalysts may include silica supports.
[0009] Metal-supported catalysts can be treated with ammonia at temperatures of 300°C or lower using ammonia gas.
[0010] The reduction reaction can be carried out under solvent-free conditions.
[0011] The reduction reaction can be carried out under hydrogen conditions of 1 bar to 100 bar and at temperatures of 150°C to 200°C.
[0012] The reduction reaction can take 0.5 to 5 hours.
[0013] The amount of metal-supported catalyst used relative to the total weight of menthol prepared can be from 0.01% to 10% by weight.
[0014] The conversion rate of thymol can be 95% or higher.
[0015] The yield of the menthol isomer mixture can be 95% or higher.
[0016] A mixture of menthol isomers may include menthol, isomenthol, neomenthol, and neoisomenthol.
[0017] The selectivity of menthol relative to a mixture of menthol isomers can be 50% or higher.
[0018] Beneficial effects of the invention One method for preparing menthol according to one aspect simultaneously achieves excellent reaction rate, menthol selectivity, and byproduct formation inhibition, even under solvent-free conditions. Specifically, the method for preparing menthol according to one aspect can effectively suppress hydrocarbon byproducts generated during the reduction of thymol, while maintaining an excellent reaction rate even at low temperatures and low catalyst dosages, and can improve the selectivity of menthol relative to menthol isomers.
[0019] Furthermore, according to one aspect, the process can be further simplified by using a small amount of catalyst under non-solvent conditions, and menthol can be prepared in high yield even under mild reaction conditions, thus significantly improving productivity. Detailed Implementation
[0020] All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. The terminology used herein is intended to effectively describe particular embodiments and should not be construed as limiting this disclosure.
[0021] As used in this article, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well.
[0022] Throughout this specification, the terms “comprising,” “including,” “containing,” or “having” do not exclude other components, but rather mean that other components may be further included unless otherwise expressly stated to the contrary, and do not exclude elements, materials, or methods not further listed.
[0023] The numerical ranges used in this paper include lower and upper limits, all values within the range, increments logically derived from the form and width of the defined range, all double-limited values, and all possible combinations of upper and lower limits of numerical ranges limited in different forms. Unless otherwise defined herein, values outside the defined numerical range that may occur due to experimental error or rounding are also intended to be included within the defined numerical ranges.
[0024] Unless otherwise defined herein, “about” may be considered to be within 30%, 25%, 20%, 15%, 10% or 5% of the stated value.
[0025] The present disclosure will now be described in detail. However, this is merely an example, and the present disclosure is not limited to the specific embodiments described as examples.
[0026] While the hydrogenation of thymol (2-isopropyl-5-methylphenol) is a widely used industrial method for preparing menthol, the hydrogenation of thymol produces a mixture of menthol isomers and hydrocarbon byproducts, resulting in low selectivity. Therefore, various studies have been conducted to improve the selectivity of menthol, but methods involving multiple steps or reducing the reaction rate lead to excessive processing time and low conversion rates, hindering commercialization. Furthermore, even methods that enhance the hydrogenation reactivity suffer from limitations such as excessive byproduct formation.
[0027] Therefore, this disclosure provides a method for preparing menthol that ensures an excellent reaction rate while satisfying excellent menthol selectivity and byproduct formation inhibition.
[0028] One method for preparing menthol may include: preparing menthol by reduction of thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.
[0029] Specifically, a method for preparing menthol according to one aspect may include: (a) treating a metal-supported catalyst with ammonia; (b) obtaining menthol by hydrogenation (reduction) of thymol in the presence of a metal-supported catalyst treated with ammonia and hydrogen.
[0030] Ammonia treatment may include treatment with aqueous ammonia solution (NH4OH), vapor of aqueous ammonia solution, or ammonia gas (NH3).
[0031] There are no particular restrictions on the temperature during ammonia treatment, but it can be, for example, 300°C or lower, or 10°C to 300°C, or 10°C to 200°C, or 10°C to 100°C, or 20°C to 100°C, or 20°C to 80°C.
[0032] According to one aspect, a metal-supported catalyst can be formed by supporting an active metal on a support to form a composite. The active metal can be, for example, one or more selected from ruthenium, iron, nickel, cobalt, platinum, palladium, vanadium, copper, chromium, tungsten, molybdenum, iridium, rhodium, zirconium, cobalt, zinc, calcium, and their oxides. Specifically, according to one aspect, a metal-supported catalyst can be a nickel-supported catalyst comprising at least one active metal selected from nickel (Ni) and nickel oxide (NiO).
[0033] The support can be one or more selected from silica, alumina, magnesium chloride, calcium chloride, bauxite, zeolite, magnesium oxide, zirconium oxide, titanium oxide, boron trioxide, calcium oxide, zinc oxide, barium oxide, and thorium oxide; specifically, it can be silica. Specifically, according to one aspect, the metal-supported catalyst can be a nickel-silica-supported catalyst, comprising an active metal such as nickel, nickel oxide, or a combination thereof supported on a silica support to form a composite.
[0034] For example, relative to 100 parts by weight of active metal, a metal-supported catalyst may include 5 to 50 parts by weight, 5 to 40 parts by weight, or 10 to 40 parts by weight of a support. Specifically, when the metal-supported catalyst according to one aspect is a nickel-silica-supported catalyst, wherein an active metal comprising nickel and nickel oxide is supported on a silica support to form a composite, the metal-supported catalyst may include 50% to 70% by weight of nickel, 10% to 30% by weight of nickel oxide, and 50% to 60% by weight of silica relative to the total weight of the catalyst, and more specifically, may include 50% to 60% by weight of nickel, 15% to 25% by weight of nickel oxide, and 15% to 25% by weight of silica.
[0035] According to one aspect, the metal-supported catalyst may further include one or more promoters, and when the metal-supported catalyst further includes promoters, the promoters may be included in an amount of 0.1 to 3.0 parts by weight relative to 100 parts by weight of active metal, thereby further improving catalytic activity.
[0036] In addition, one method for preparing menthol can be carried out under solvent-free conditions.
[0037] In other words, the method for preparing menthol according to one aspect can simultaneously achieve excellent reaction rate, menthol selectivity, and byproduct inhibition even under solvent-free conditions. Specifically, the method for preparing menthol according to one aspect can achieve excellent reaction rate even at low temperature and low catalyst dosage, achieving a thymol conversion rate of nearly 100% in a short time, effectively inhibiting the formation of byproducts, and achieving high selectivity of menthol relative to menthol isomers.
[0038] For example, a reduction reaction according to one aspect can be carried out under conditions of hydrogen gas at 1 bar to 100 bar and temperature at 100°C to 200°C, or hydrogen gas at 1 bar to 50 bar and temperature at 150°C to 200°C, or hydrogen gas at 1 bar to 30 bar and temperature at 160°C to 190°C.
[0039] For example, the amount of metal-supported catalyst used may be 0.01% to 20% by weight, or 0.01% to 15% by weight, or 0.01% to 10% by weight, or 0.1% to 10% by weight, or 2% to 10% by weight, relative to the total weight of the resulting menthol isomer mixture.
[0040] For example, the reduction reaction in one aspect can be carried out under the above conditions for 0.5 to 5 hours, 0.5 to 3 hours, or 0.1 to 2 hours.
[0041] For example, in a method for preparing menthol according to one aspect, the conversion rate of thymol ((amount of thymol added - amount of thymol remaining after reaction) / amount of thymol added × 100) can be 90% or higher, or 95% or higher, or 98% or higher, and in particular can be 100%.
[0042] For example, in a method for preparing menthol according to one aspect, the yield of the mixture of menthol isomers may be 80% or higher, or 85% or higher, or 90% or higher, or 95% or higher, and in this respect, the upper limit may be 99% or lower, or 98% or lower.
[0043] A mixture of menthol isomers may include menthol, isomenthol, neomenthol, and neoisomenthol.
[0044] For example, in a method for preparing menthol according to one aspect, the selectivity of menthol relative to a mixture of menthol isomers ((menthol production / menthol isomer production) × 100) can be 30% or higher, or 40% or higher, or 50% or higher, with an upper limit of 95% or lower, or 90% or lower, or 80% or lower.
[0045] The above-described embodiments will be described in more detail below through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the claims.
[0046] [Preparation Example] Preparation of metal-supported catalysts 300m² 240g of porous silica powder with a pore size of 21nm and an average particle size of 7μm, 491g of nickel sulfate (LiSO4), 6g of copper sulfate (CuSO4), and 2000mL of distilled water were placed in a precipitation tank and stirred until the temperature reached 80℃. After reaching 80℃, 1500mL of a solution containing 262g of sodium carbonate (Na2CO3) was injected over 1 hour using a syringe pump. After precipitation, the pH of the slurry was 7.6. It was washed with approximately 30L of distilled water and filtered, then dried in a drying oven at 100℃ for 12 hours or longer. The dried material was divided into small portions and then calcined in air at 350℃. The calcined material was again divided into small portions and activated in a hydrogen atmosphere at a lower temperature of 350℃. The activated catalyst was immobilized using a nitrogen gas mixture containing 1% oxygen to prepare a nickel-silica supported catalyst.
[0047] [Example 1] Preparation of metal-supported catalysts for ammonia treatment The nickel-silica supported catalyst obtained in the preparation example was added to the reactor, and the reactor was then purged with nitrogen at a flow rate of 7.5 ml / min per g of catalyst. Then, while maintaining the temperature at 20°C, the reaction was treated for 30 minutes with ammonia (NH3) diluted to 10% in helium (He) at a flow rate of 5 ml / min per g of catalyst, followed by another nitrogen purging to obtain the ammonia-treated nickel-silica supported catalyst. All these processes were carried out under atmospheric pressure.
[0048] Preparation of menthol 300 g of thymol was added to an autoclave, and the temperature of the autoclave was raised to below 60 °C. While the thymol was melting, 4.5 g of the ammonia-treated nickel-silica supported catalyst obtained above was added and the autoclave was sealed. After sequential purging with nitrogen and hydrogen, the reactor was filled with hydrogen until the pressure reached 2 bar, and stirred at 1600 rpm with a gas-phase induction hollow stirrer, and heated to 160 °C. When the internal temperature of the reactor reached 160 °C, hydrogen was added at 10 bar and the temperature was raised to 170 °C, and the reaction was carried out while maintaining the temperature and pressure. Samples were collected at each reaction time, and the residual thymol content, the content of the intermediate (menthone), menthol isomers, and hydrocarbon byproducts (menthane) were analyzed by gas chromatography (column: CP-ChiraSil-DEX CB (CP7502)). The results are shown in Table 1 below.
[0049] [Example 2] The amount of catalyst was changed to 18g, and the reaction temperature was changed to 180°C. Otherwise, the process was carried out in the same manner as in Example 1.
[0050] [Example 3] The reaction temperature was changed to 190°C, otherwise the process was carried out in the same manner as in Example 2.
[0051] [Comparative Example 1] The nickel-silica supported catalyst obtained in the preparation example was used instead of the ammonia-treated nickel-silica supported catalyst, and otherwise the process was carried out in the same manner as in Example 1.
[0052] [Table 1]
[0053] Referring to Table 1 above, it can be seen that the preparation method according to the examples has an excellent reaction rate and simultaneously satisfies the requirements of hydrocarbon byproduct formation inhibition and menthol selectivity. On the other hand, the preparation method of the comparative examples was carried out at the same reaction temperature as in Example 1, but thymol was not completely converted within 3 hours, hydrocarbon byproducts increased significantly over time, and the menthol selectivity was also significantly reduced compared to the examples.
[0054] While this disclosure has been described with reference to the limited embodiments described above, these embodiments are provided only to facilitate a more general understanding of the disclosure. This disclosure is not limited to the above embodiments, and various modifications and variations can be made by those skilled in the art based on these descriptions.
[0055] Therefore, the scope of this disclosure should not be limited to the described embodiments, nor to the appended claims, but to all embodiments having the same or equivalent variations as the claims.
Claims
1. A method for preparing menthol, the method comprising: Menthol was prepared by the reduction of thymol in the presence of an ammonia-treated metal-supported catalyst and hydrogen.
2. The method according to claim 1, wherein, The metal-supported catalyst includes a nickel-supported catalyst, wherein the nickel-supported catalyst comprises one or more active metals selected from nickel and nickel oxide.
3. The method according to claim 2, wherein, The metal-supported catalyst includes a silica support.
4. The method according to claim 1, wherein, The metal-supported catalyst is treated with ammonia at a temperature of 300°C or lower using ammonia gas.
5. The method according to claim 1, wherein, The reduction reaction is carried out under solvent-free conditions.
6. The method according to claim 1, wherein, The reduction reaction is carried out under hydrogen conditions of 1 bar to 100 bar and at a temperature of 150°C to 200°C.
7. The method according to claim 1, wherein, The reduction reaction is carried out for 0.5 to 5 hours.
8. The method according to claim 1, wherein, The amount of the metal-supported catalyst used is from 0.01% to 10% by weight relative to the total weight of the menthol prepared.
9. The method according to claim 1, wherein, The conversion rate of thymol is 95% or higher.
10. The method according to claim 9, wherein, The yield of the menthol isomer mixture is 95% or higher.
11. The method according to claim 10, wherein, The mixture of menthol isomers includes menthol, isomenthol, neomenthol, and neoisomenthol.
12. The method according to claim 11, wherein, The selectivity of menthol relative to the mixture of menthol isomers is 50% or higher.